Present construction techniques include foundations formed from deep routed support columns referred to as piles. Current pile technology falls into two basic types: (1) driven piles, which are pounded into the earth by a series of blows from an automated hammer; and (2) auger cast piles, which are formed by drilling into the earth with an auger and backfilling the resulting hole with concrete as the auger is withdrawn. It should be noted that driven piles are typically made of steel, timber, or concrete.
Larger equipment and higher design loads are often specified to minimize the number of piles and reduce project costs. Therefore, performance of each foundation element is more critical, requiring additional quality assurance for every element of a project. It is easily recognized that quality is involved in the success or failure of any project. Since projects built on deep foundations require that a support system be properly installed, failure of any component could result in the failure of the entire project regardless of how carefully the above ground structure is built. Individual inspection of driven or cast-in-situ piles is practically impossible after installation, and thus quality control during pile installation is of great importance. Accordingly, most construction codes specify proper recording of installation observations. Many companies require total quality management (TQM) for risk management to reduce legal liability.
In the past, manual visual observations of blow count or drilling progress, followed by static testing of a small sample of piles, were often the only available construction quality control methods. There are numerous drawbacks to a manual recording system. In this respect, manually recorded observations are only as reliable as the observer, and thus numerous errors were common. For instance, counting blows during pile driving is monotonous, and lack of concentration or interference with the inspector caused inadvertent errors in counting.
The accuracy of both blow count and/or pile penetration was frequently very poor when reference marks were inaccurately drawn on the pile. The blow count for pile driving was often recorded for relatively large increments (i.e., blows per 250 millimeters, or blows per foot), and the pile was driven farther than necessary to assure consistent blow count. If the equivalent blow count over a smaller interval (or several successive smaller intervals to assess consistency), could be reliably taken, then the accuracy and economy of the project could both be significantly improved.
Furthermore, the field records were often transcribed for legibility, potentially compounding errors, particularly when the original field records were difficult to read. In addition, the recorded data was subject to abuse by alterations. Moreover, manual recording is a labor intensive process, and therefore expensive.
Static loading tests are performed on a small number of piles to at least twice the design load in order to prove the foundation design. Because of the high cost of failure, test piles are often purposefully driven harder or farther than necessary. As a result, proof tests usually pass easily, with the actual safety factors being higher than required. Production piles then use the same very conservative criteria, resulting in higher than necessary costs. In numerous cases the static tests are avoided due to high costs, unwanted construction delays, or because they are practically impossible for piles in deep water. While extra care is generally given in driving a test pile, production piles are often installed with less care, and thus may not achieve the same quality.
Current manual inspection reports often provide incomplete information and/or contain errors due to fast hammer speed, high number of blows and the monotonous nature of the task. Since errors are unacceptable, it is desirable to record the installation both automatically and accurately. Moreover, other important observations often neglected include actual hammer performance, pile inclination angle, start-interruption and/or end of driving times, pile cushion change, section length, and the like. Accordingly, there is a need for a pile installation recording system for driven piles, which automatically and accurately acquires data, and which provides accurate and comprehensive installation reports.
In the case of auger cast piles, there has been a reluctance to increase loads due to cross section uncertainties. In this respect, auger cast pile quality is very dependent upon the skill of the installation crew. If the continuous flight auger (CFA) is withdrawn too rapidly, the concrete volume will be reduced and the structural strength of the shaft may be insufficient. For auger cast piles, manual inspection is extremely difficult and therefore either minimal or even totally lacking. Determination of concrete volume can be perhaps made by counting cycles of the grout pump and calibrating the volume of each cycle. Even if this is accomplished the task must be coordinated with the auger withdrawal rate and this complexity means it is an almost impossible task to determine with any reasonable accuracy the volume pumped per unit depth. The shaft quality is totally dependent upon the skill of the contractor. The volume precision is insufficient for smaller diameter shafts. The "counting" is easily abused and the resulting manual inspection is usually at best a wild guess and not considered reliable by the engineer responsible for the project. In many cases, high safety factors are assigned to reduce this risk, making auger cast piles uneconomic. Accordingly, there is a need for a pile installation recording system for auger cast piles, which automatically and accurately acquires data for every auger cast pile during installation, and which provides accurate and comprehensive installation reports. This will increase the specifying engineer's confidence in the integrity of auger cast piles. As a result, auger cast piles will be more cost effective and more widely accepted at various project sites.
The present invention addresses the drawbacks of prior art manual recording methods, and provides significant improvements to existing electronic pile installation recording systems.